Evolution of the Alfvén Mach number associated with a coronal mass ejection shock

The Sun regularly produces large-scale eruptive events, such as coronal mass ejections (CMEs) that can drive shock waves through the solar corona. Such shocks can result in electron acceleration and subsequent radio emission in the form of a type II radio burst. However, the early-phase evolution of shock properties and its relationship to type II burst evolution is still subject to investigation. Here we study the evolution of a CME-driven shock by comparing three commonly used methods of calculating the Alfvén Mach number (MA), namely: shock geometry, a comparison of CME speed to a model of the coronal Alfvén speed, and the type II band-splitting method. We applied the three methods to the 2017 September 2 event, focusing on the shock wave observed in extreme ultraviolet by the Solar Ultraviolet Imager on board GOES-16, in white-light by the Large Angle and Spectrometric Coronagraph on board SOHO, and the type II radio burst observed by the Irish Low Frequency Array. We show that the three different methods of estimating shock MA yield consistent results and provide a means of relating shock property evolution to the type II emission duration. The type II radio emission emerged from near the nose of the CME when MA was in the range 1.4–2.4 at a heliocentric distance of ∼1.6 R⊙. The emission ceased when the CME nose reached ∼2.4 R⊙, despite an increasing Alfvén Mach number (up to 4). We suggest the radio emission cessation is due to the lack of quasi-perpendicular geometry at this altitude, which inhibits efficient electron acceleration and subsequent radio emission.

Download Full-text

Evolution of the Alfvén Mach number associated with a coronal mass ejection shock

10.5194/egusphere-egu2020-11425 ◽

2020 ◽

Author(s):

Ciara Maguire ◽

Eoin Carley ◽

Joseph McCauley ◽

Peter Gallagher

Keyword(s):

Mach Number ◽

Radio Emission ◽

Radio Burst ◽

Large Scale ◽

Extreme Ultraviolet ◽

Splitting Method ◽

Large Angle ◽

Electron Acceleration ◽

Phase Evolution ◽

Type Ii

The Sun regularly produces large-scale eruptive events, such as coronal mass ejections (CMEs) that can drive shock waves through the solar corona. Such shocks can result in electron acceleration and subsequent radio emission in the form of a type II radio burst. However, the early-phase evolution of shock properties and its relationship to type II burst evolution is still subject to investigation. Here we study the evolution of a CME-driven shock by comparing three commonly used methods of calculating the Alfv&#233;n Mach number (MA), namely: shock geometry, a comparison of CME speed to a model of the coronal Alfv&#233;n speed, and the type II band-splitting method. We applied the three methods to the 2017 September 2 event, focusing on the shock wave observed in extreme ultraviolet (EUV) by the Solar Ultraviolet Imager (SUVI) on board GOES-16, in white-light by the Large Angle and Spectrometric Coronagraph (LASCO) on board SOHO, and the type II radio burst observed by the Irish Low Frequency Array (I-LOFAR). We show that the three different methods of estimating shock MA yield consistent results and provide a means of relating shock property evolution to the type II emission duration. The type II radio emission emerged from near the nose of the CME when MA&#160;was in the range 1.4-2.4 at a heliocentric distance of&#160;&#8764;1.6&#160;R&#8857;. The emission ceased when the CME nose reached&#160;&#8764;2.4&#160;R&#8857;, despite an increasing Alfv&#233;n Mach number (up to 4). We suggest the radio emission cessation is due to the lack of quasi-perpendicular geometry at this altitude, which inhibits efficient electron acceleration and subsequent radio emission.

Download Full-text

Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732308 ◽

2018 ◽

Vol 615 ◽

pp. A89 ◽

Cited By ~ 24

Author(s):

P. Zucca ◽

D. E. Morosan ◽

A. P. Rouillard ◽

R. Fallows ◽

P. T. Gallagher ◽

...

Keyword(s):

Radio Emission ◽

Radio Burst ◽

Second Harmonic ◽

3D Structure ◽

Large Angle ◽

Type Ii ◽

Polytropic Model ◽

Coronal Shock ◽

Observational Uncertainty ◽

Harmonic Source

Context. Type II radio bursts are evidence of shocks in the solar atmosphere and inner heliosphere that emit radio waves ranging from sub-meter to kilometer lengths. These shocks may be associated with coronal mass ejections (CMEs) and reach speeds higher than the local magnetosonic speed. Radio imaging of decameter wavelengths (20–90 MHz) is now possible with the Low Frequency Array (LOFAR), opening a new radio window in which to study coronal shocks that leave the inner solar corona and enter the interplanetary medium and to understand their association with CMEs. Aims. To this end, we study a coronal shock associated with a CME and type II radio burst to determine the locations at which the radio emission is generated, and we investigate the origin of the band-splitting phenomenon. Methods. Thetype II shock source-positions and spectra were obtained using 91 simultaneous tied-array beams of LOFAR, and the CME was observed by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) and by the COR2A coronagraph of the SECCHI instruments on board the Solar Terrestrial Relation Observatory(STEREO). The 3D structure was inferred using triangulation of the coronographic observations. Coronal magnetic fields were obtained from a 3D magnetohydrodynamics (MHD) polytropic model using the photospheric fields measured by the Heliospheric Imager (HMI) on board the Solar Dynamic Observatory (SDO) as lower boundary. Results. The type II radio source of the coronal shock observed between 50 and 70 MHz was found to be located at the expanding flank of the CME, where the shock geometry is quasi-perpendicular with θBn ~ 70°. The type II radio burst showed first and second harmonic emission; the second harmonic source was cospatial with the first harmonic source to within the observational uncertainty. This suggests that radio wave propagation does not alter the apparent location of the harmonic source. The sources of the two split bands were also found to be cospatial within the observational uncertainty, in agreement with the interpretation that split bands are simultaneous radio emission from upstream and downstream of the shock front. The fast magnetosonic Mach number derived from this interpretation was found to lie in the range 1.3–1.5. The fast magnetosonic Mach numbers derived from modelling the CME and the coronal magnetic field around the type II source were found to lie in the range 1.4–1.6.

Download Full-text

LOFAR observations of a jet-driven piston shock in the low solar corona

10.5194/egusphere-egu21-7602 ◽

2021 ◽

Author(s):

Ciara Maguire ◽

Eoin Carley ◽

Pietro Zucca ◽

Nicole Vilmer ◽

Peter Gallagher

Keyword(s):

Radio Burst ◽

Extreme Ultraviolet ◽

Large Angle ◽

Low Frequency ◽

Density Fluctuations ◽

Plasma Emission ◽

Type Ii ◽

Radio Waves ◽

Type Ii Radio Bursts ◽

Electron Density Fluctuations

The Sun produces highly dynamic and eruptive events that can drive shocks through the corona. These shocks can accelerate electrons, which result in plasma emission in the form of a type II radio burst. Despite a large number of type II radio bursts observations, the precise origin of coronal shocks is still subject to investigation. Here we present a well-observed solar eruptive event that occurred on 16 October 2015, focusing on a jet observed in the extreme ultraviolet by the SDO Atmospheric Imaging Assembly, a streamer observed in white-light by the Large Angle and&#160; Spectrometric Coronagraph, and a metric type II radio burst observed by the LOw-Frequency Array (LOFAR) radio telescope. For the first time, LOFAR has interferometrically imaged the fundamental and harmonic sources of a type II radio burst and revealed that the sources did not appear to be co-spatial, as would be expected from the plasma emission mechanism. We correct for the separation between the fundamental and harmonic using a model which accounts for the scattering of radio waves by electron density fluctuations in a turbulent plasma. This allows us to show the type II radio sources were located &#8764;0.5 Rsun above the jet and propagated at a speed of &#8764;1000 km s&#8722;1, which was significantly faster than the jet speed of &#8764;200 km s&#8722;1. This suggests that the type II burst was generated by a piston shock driven by the jet in the low corona.

Download Full-text

VLBI for probing large-scale magnetic structures of stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900083200 ◽

1996 ◽

Vol 176 ◽

pp. 173-180

Author(s):

J.-F. Lestrade

Keyword(s):

Magnetic Fields ◽

Radio Emission ◽

Large Scale ◽

Electron Acceleration ◽

High Gravity ◽

Magnetic Structures

By VLBI astrometry, we show that the two RSCVn type binaries, UX Ari and σ2 CrB, have a preferred site of radio emission which is the intra-system region. It is known that radio emission from these stars is from the gyro-synchrotron process associated with large-scale magnetic fields. High gravity in the intra-system region might favor dense magnetic loops. Interactions in this region between loops attached to the surfaces of the two stellar components might produce reconnections required for electron acceleration.

Download Full-text

Electron acceleration and type II radio emission at quasi-parallel shock waves

Radiophysics and Quantum Electronics ◽

10.1007/bf02676712 ◽

1998 ◽

Vol 41 (1) ◽

pp. 53-67

Author(s):

H. -T. Claßen ◽

G. Mann

Keyword(s):

Shock Waves ◽

Radio Emission ◽

Electron Acceleration ◽

Type Ii

Download Full-text

A SOLAR TYPE II RADIO BURST FROM CORONAL MASS EJECTION-CORONAL RAY INTERACTION: SIMULTANEOUS RADIO AND EXTREME ULTRAVIOLET IMAGING

The Astrophysical Journal ◽

10.1088/0004-637x/787/1/59 ◽

2014 ◽

Vol 787 (1) ◽

pp. 59 ◽

Cited By ~ 33

Author(s):

Yao Chen ◽

Guohui Du ◽

Li Feng ◽

Shiwei Feng ◽

Xiangliang Kong ◽

...

Keyword(s):

Coronal Mass Ejection ◽

Radio Burst ◽

Extreme Ultraviolet ◽

Type Ii ◽

Solar Type ◽

Mass Ejection

Download Full-text

Extended radio emission associated with a breakout eruption from the back side of the Sun

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936878 ◽

2020 ◽

Vol 633 ◽

pp. A141 ◽

Cited By ~ 2

Author(s):

D. E. Morosan ◽

E. Palmerio ◽

B. J. Lynch ◽

E. K. J. Kilpua

Keyword(s):

Radio Emission ◽

Radio Burst ◽

Coronal Mass Ejections ◽

Extreme Ultraviolet ◽

Particle Accelerators ◽

Back Side ◽

The Sun ◽

Radio Bursts ◽

Solar Dynamics Observatory ◽

Extended Radio

Context. Coronal mass ejections (CMEs) on the Sun are the largest explosions in the Solar System that can drive powerful plasma shocks. The eruptions, shocks, and other processes associated to CMEs are efficient particle accelerators and the accelerated electrons in particular can produce radio bursts through the plasma emission mechanism. Aims. Coronal mass ejections and associated radio bursts have been well studied in cases where the CME originates close to the solar limb or within the frontside disc. Here, we study the radio emission associated with a CME eruption on the back side of the Sun on 22 July 2012. Methods. Using radio imaging from the Nançay Radioheliograph, spectroscopic data from the Nançay Decametric Array, and extreme-ultraviolet observations from the Solar Dynamics Observatory and Solar Terrestrial Relations Observatory spacecraft, we determine the nature of the observed radio emission as well as the location and propagation of the CME. Results. We show that the observed low-intensity radio emission corresponds to a type II radio burst or a short-duration type IV radio burst associated with a CME eruption due to breakout reconnection on the back side of the Sun, as suggested by the pre-eruptive magnetic field configuration. The radio emission consists of a large, extended structure, initially located ahead of the CME, that corresponds to various electron acceleration locations. Conclusions. The observations presented here are consistent with the breakout model of CME eruptions. The extended radio emission coincides with the location of the current sheet and quasi-separatrix boundary of the CME flux and the overlying helmet streamer and also with that of a large shock expected to form ahead of the CME in this configuration.

Download Full-text

PBG Cavity in NV-Diamond for Large Scale Type II Quantum Computing

10.21236/ada422052 ◽

2004 ◽

Author(s):

Selim Shahriar

Keyword(s):

Quantum Computing ◽

Large Scale ◽

Type Ii ◽

Scale Type

Download Full-text

Experiments of Compressible Homogeneous and Isotropic Turbulence Interacting With Expansion Waves

Volume 2: Symposia, Parts A, B, and C ◽

10.1115/fedsm2003-45075 ◽

2003 ◽

Author(s):

Savvas S. Xanthos ◽

Yiannis Andreopoulos

Keyword(s):

Mach Number ◽

Shock Tube ◽

Total Pressure ◽

Large Scale ◽

Isotropic Turbulence ◽

Pressure Fluctuations ◽

Incident Shock ◽

Expansion Waves ◽

Curvature Effects ◽

Homogeneous And Isotropic Turbulence

The interaction of traveling expansion waves with grid-generated turbulence was investigated in a large-scale shock tube research facility. The incident shock and the induced flow behind it passed through a rectangular grid, which generated a nearly homogeneous and nearly isotropic turbulent flow. As the shock wave exited the open end of the shock tube, a system of expansion waves was generated which traveled upstream and interacted with the grid-generated turbulence; a type of interaction free from streamline curvature effects, which cause additional effects on turbulence. In this experiment, wall pressure, total pressure and velocity were measured indicating a clear reduction in fluctuations. The incoming flow at Mach number 0.46 was expanded to a flow with Mach number 0.77 by an applied mean shear of 100 s−1. Although the strength of the generated expansion waves was mild, the effect on damping fluctuations on turbulence was clear. A reduction of in the level of total pressure fluctuations by 20 per cent was detected in the present experiments.

Download Full-text

Large-scale structure and entrainment in the supersonic mixing layer

Journal of Fluid Mechanics ◽

10.1017/s0022112095000310 ◽

1995 ◽

Vol 284 ◽

pp. 171-216 ◽

Cited By ~ 254

Author(s):

N. T. Clemens ◽

M. G. Mungal

Keyword(s):

Mach Number ◽

High Speed ◽

Large Scale ◽

Mixture Fraction ◽

Mixing Layer ◽

Mie Scattering ◽

Planar Laser ◽

The Cross ◽

Convective Mach Number ◽

Stream Direction

Experiments were conducted in a two-stream planar mixing layer at convective Mach numbers,Mc, of 0.28, 0.42, 0.50, 0.62 and 0.79. Planar laser Mie scattering (PLMS) from a condensed alcohol fog and planar laser-induced fluorescence (PLIF) of nitric oxide were used for flow visualization in the side, plan and end views. The PLIF signals were also used to characterize the turbulent mixture fraction fluctuations.Visualizations using PLMS indicate a transition in the turbulent structure from quasi-two-dimensionality at low convective Mach number, to more random three-dimensionality for$M_c\geqslant 0.62$. A transition is also observed in the core and braid regions of the spanwise rollers as the convective Mach number increases from 0.28 to 0.62. A change in the entrainment mechanism with increasing compressibility is also indicated by signal intensity profiles and perspective views of the PLMS and PLIF images. These show that atMc= 0.28 the instantaneous mixture fraction field typically exhibits a gradient in the streamwise direction, but is more uniform in the cross-stream direction. AtMc= 0.62 and 0.79, however, the mixture fraction field is more streamwise uniform and with a gradient in the cross-stream direction. This change in the composition of the structures is indicative of different entrainment motions at the different compressibility conditions. The statistical results are consistent with the qualitative observations and suggest that compressibility acts to reduce the magnitude of the mixture fraction fluctuations, particularly on the high-speed edge of the layer.

Download Full-text